A BP-Au-MS2 ternary gas-sensitive composite material and its application

Abstract

The present invention belongs to the field of gas sensitive materials, and specifically relates to a BP-Au-MS2 ternary gas-sensitive composite material and its application. Among them, BP-Au-MS2 is a ternary composite material containing gold, black phosphorus and transition metal sulfide. The preparation method is as follows: (1) Mixing transition metal salt, oxalic acid and thiourea evenly under acidic conditions; (2) Reacting the reaction system under high temperature conditions to obtain transition metal sulfide; (3) Attaching gold particles to the surface of transition metal sulfide by chloroauric acid. (4) Using gold-containing transition metal sulfide, red phosphorus, solid iodine and selenium powder as raw materials, high-temperature vacuum sintering is performed to obtain the target product. The target is a room-temperature gas-sensitive material that is highly sensitive to different concentrations of NO, NO2 or NH3, which has the advantages of high sensitivity, can be used at room temperature, good stability and strong oxidizability. It is suitable for preparing various types of gas sensors, gas detectors or alarms. The present invention overcomes the defects of poor stability and insufficient sensitivity of black phosphorus materials.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensitive materials, and specifically relates to a BP-Au-MS2 ternary gas-sensitive composite material, a gas-sensitive element developed based on the BP-Au-MS2 ternary gas-sensitive composite material, a NO2 concentration detector, and a harmful gas alarm. Background Art

[0002] A large amount of fossil fuels are consumed in the process of industrial production and transportation. The use of fossil fuels will initially emit a large amount of carbon dioxide and cause global warming. In addition, a large amount of toxic and harmful gases may also be emitted, such as nitrogen oxides, ammonia, sulfide gases, etc. If these gases are emitted into the atmosphere in large quantities, they may cause a serious ecological crisis. Therefore, controlling the emission of harmful gases is one of the most important tasks of the environmental protection department. The premise of controlling the emission of harmful gases is to be able to effectively detect harmful gases, which requires the use of certain gas sensors that are highly sensitive to specific gases. In addition to the need for industrial production to monitor the gas composition and concentration of exhaust gases, with the improvement of the quality of life, people's demand for the detection of toxic and harmful gases such as NH3, NO2, formaldehyde, acetone, etc. in living and office environments is also increasing. This requires technicians to develop various high-performance gas sensitive materials.

[0003] At present, the sensor sensitive materials commonly used in the field of gas detection mainly include metal oxides and mixed metal oxides such as In2O3, ZnO, SnO2, and WO3. However, the working temperature of metal oxide sensing materials is often 200-500℃, and they need to be heated in the sensor before they can be used. They are very limited in application scenarios and are not suitable for detecting flammable and explosive organic volatiles. They are mostly used in industrial production. In addition, this type of sensor also generally has defects such as high energy consumption, low safety, and limited service life.

[0004] A gas sensor and its preparation method are disclosed in the document of China Invention Patent Authorization Announcement No. CN106841338B. This method uses black phosphorus material doped with metal cobalt as a gas sensitive material; and uses the special semiconductor band gap and special chemical activity of black phosphorus material to achieve high-precision measurement of carbon monoxide gas at room temperature. However, since black phosphorus material is very easy to decompose in the air, the stability of the gas sensitive material is poor and the service life of the gas sensitive element is short. This will also limit the industrial application prospects of this solution.

[0005] Therefore, how to develop a gas-sensitive material with better adaptability to different application environments and stronger stability in structure and performance is becoming a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0006] In order to solve the problems of poor stability, short service life, insufficient reliability of measurement accuracy, etc. of conventional black phosphorus gas-sensitive materials, the present invention provides a BP-Au-MS2 ternary gas-sensitive composite material, a gas-sensitive element, a NO2 concentration detector, and a harmful gas alarm developed based on the BP-Au-MS2 ternary gas-sensitive composite material.

[0007] The present invention is implemented by the following technical solutions:

[0008] The present invention prepares a novel BP-Au-MS2 ternary gas-sensitive composite material, which is a ternary composite material containing gold, black phosphorus and transition metal sulfide. Specifically, the preparation method of the BP-Au-MS2 ternary gas-sensitive composite material is as follows:

[0009] (1) Prepare transition metal salt, oxalic acid, and thiourea in a mass ratio of 1:(1-1.5):(1.7-2). Add the transition metal salt to a sufficient amount of deionized water and stir to dissolve, and adjust the pH of the solution to 1.2-1.5 with hydrochloric acid and continue stirring for 15 minutes. Then, add oxalic acid to the above solution and stir for 10 minutes, then add thiourea and stir for 30 minutes to obtain a uniformly mixed reaction system.

[0010] (2) The reaction system in the above step is transferred to a reactor and reacted at a temperature of 220-250° C. for 24 hours. The precipitate generated by the reaction is centrifuged and washed, and vacuum dried for 8 hours to obtain a transition metal sulfide.

[0011] (3) Add the transition metal sulfide from the previous step to a sufficient amount of ethanol solution, and add HAuCl4 in a mass ratio of HAuCl4 to transition metal sulfide of 5:1. Ultrasonicate the mixture for 2 hours and then stir for 8 to 12 hours; centrifuge and wash to obtain a solid, vacuum dry for 8 hours, and obtain a gold-containing transition metal sulfide powder.

[0012] (4) The gold-containing transition metal sulfide obtained in the above step is mixed with red phosphorus, solid iodine, and selenium powder in a mass ratio of 1: (0.5-2): (0.05-0.2): (0.025-0.1). The mixture is vacuum fired, and the temperature control conditions of the vacuum firing process are as follows: first, the temperature is raised to 590-620°C at 5°C / min and kept for 2h, and then the temperature is reduced to 500°C at 0.6-0.8°C / min and kept for 5h, then the temperature is reduced to 200°C at 1°C / min, and finally naturally cooled to obtain the BP-Au-MS2 ternary gas-sensitive composite material.

[0013] As a further improvement of the present invention, in step (1), the transition metal salt is selected from any one of sodium tungstate dihydrate, tungsten chloride, and sodium molybdate dihydrate.

[0014] As a further improvement of the present invention, the vacuum drying process of the product in steps (2) and (3) is completed in a vacuum oven, and the drying temperature is set to 60°C.

[0015] As a further improvement of the present invention, in step (3), the mixture containing transition metal sulfide, HAuCl4 and ethanol solution is ultrasonically dispersed by an ultrasonic disperser, and the ultrasonic power of the ultrasonic disperser is 300W to 500W and the frequency is 40KHz.

[0016] As a further improvement of the present invention, in step (4), the vacuum firing method of the mixture of the transition metal sulfide containing gold and red phosphorus, solid iodine and selenium powder is as follows: the mixture is sent to a quartz tube, vacuum-sealed, and then the quartz tube is placed in a muffle furnace for firing.

[0017] The present invention also provides an application of a BP-Au-MS2 ternary gas-sensitive composite material. Specifically, the gas-sensitive material can be used to prepare a gas-sensitive probe or a trace gas detection element. Then, the qualitative or quantitative detection of the target gas at the ppb level can be achieved under room temperature conditions. The BP-Au-MS2 ternary gas-sensitive composite material provided by the present invention has a strong sensitivity to both nitrogen oxide gases (such as nitrogen dioxide and nitric oxide) and ammonia, so the target gases detected include nitrogen oxide gases and ammonia. In particular, since the BP-Au-MS2 ternary gas-sensitive composite material has the strongest sensitivity to nitrogen dioxide, the target gas is preferably NO2.

[0018] The present invention also includes a gas sensor, which is a sensitive electrode whose resistance changes with the change of the concentration of the target gas in the ambient atmosphere; the sensitive electrode includes a Pt interdigital electrode containing an aluminum oxide substrate, and a sensitive layer located on the surface of the Pt interdigital electrode. The material of the sensitive layer adopts the BP-Au-MS2 ternary gas-sensitive composite material as mentioned above.

[0019] The preparation method of the gas sensor is as follows:

[0020] The BP-Au-MS2 ternary gas-sensitive composite material was added to ethanol and subjected to ultrasonic dispersion treatment for 1 to 5 minutes. The suspension was then dropped onto a Pt interdigital electrode containing an alumina substrate and dried to obtain the desired gas-sensitive element containing a sensitive layer.

[0021] The present invention also includes a NO2 concentration detector, which uses the aforementioned gas sensor as a detection electrode to form a dynamic four-channel gas-sensitive test system. The data processing module in the NO2 concentration detector outputs the currently detected NO2 concentration value according to the acquired real-time resistance value R of the detection electrode and the pre-constructed gas response function Q.

[0022] In the NO2 concentration detector, the gas response function is generated as follows:

[0023] S1: Prepare the gas sensor as described above; and use the gas sensor as a detection electrode to form a dynamic four-channel gas sensing test system.

[0024] S2: Create a sealed gas detection environment and place the detection electrodes of the dynamic four-channel gas sensitive test system in the gas detection environment.

[0025] S3: According to the preset NO2 concentration measurement points, the dynamic four-channel gas-sensitive test system is used to cycle the response and recovery test to obtain the response-recovery curve. The response and recovery test includes the following process:

[0026] S31: Set multiple discrete measuring points according to the measuring range of the NO2 concentration detector; each measuring point includes a corresponding NO2 concentration Q i .

[0027] S32: According to NO2 concentration Q i The measuring points are sorted from small to large to obtain a measuring point queue to be filled.

[0028] S33: In the initial state, the gas filled in the gas detection environment is air, and the initial resistance value Ra of the detection electrode at the current moment is recorded. i .

[0029] S34: Select the initial measuring point of the measuring point queue as the current measuring point, and fill NO2 into the gas detection environment until the gas concentration reaches the NO2 concentration Q at the current measuring point. i Observe the decrease in the resistance of the detection electrode and record the lowest resistance value Rg under the current gas detection state. i . Complete the measurement task of the current measuring point and replace the gas in the gas detection environment with air.

[0030] S34: Select the next measuring point in the measuring point array queue as the current measuring point, repeat steps S33-S35, and execute the cycle to measure Ra in the air. i , measure Rg when NO2 reaches the current measuring point i The operation is repeated until the measurement tasks of all measuring points in the measuring point queue are completed.

[0031] At this time, the recorded resistance change waveform of the detection electrode is the required response-recovery curve.

[0032] S4: According to the data corresponding to each measuring point in the response-recovery curve in the previous step, the resistance change rate S corresponding to each measuring point is calculated by the following formula: i :

[0033]

[0034] S4: Based on the Q of a series of discrete measurement points obtained from the response-recovery curve i and S i The mapping relationship between them is used to fit a corresponding gas response function. The form of the gas response function is as follows:

[0035]

[0036] In the above formula, Q represents the detection result output by the NO2 concentration detector in real time, R represents the real-time resistance value of the detection electrode, R0 represents the resistance value of the detection electrode in the air; S represents the resistance change rate of the detection electrode under the current environment.

[0037] The present invention also includes a harmful gas alarm, which is used to monitor the comprehensive concentration of ammonia and nitrogen oxide gases in the target space in real time and issue an alarm when the concentration detection value exceeds a preset upper limit. The harmful gas alarm includes: a sensitive element, a detection circuit, a data processing module, and an alarm device.

[0038] Among them, the sensitive element adopts the gas sensitive element as mentioned above. The detection circuit is used to collect the real-time resistance value of the sensitive element. The data processing module includes a calculation unit and a comparison unit. The calculation unit is used to calculate the resistance change rate S of the current state of the sensitive element relative to the initial state according to the real-time resistance value collected by the detection circuit. The comparison unit is used to compare whether the resistance change rate S is a preset safety upper limit Smax. When S>Smax, a warning signal is output, and when S≤Smax, a safety signal is output. The alarm device is used to receive the output signal of the comparison unit in the data processing module, and when the received output signal is a warning signal, it sends an alarm indicating that the concentration of dangerous gas exceeds the limit.

[0039] The technical solution provided by the present invention has the following beneficial effects:

[0040] The present invention has developed a ternary BP-Au-MS2 gas-sensitive composite material comprising passivated black phosphorus, gold, and transition metal sulfide, and provides a preparation process of the BP-Au-MS2 ternary gas-sensitive composite material. The BP-Au-MS2 ternary gas-sensitive composite material developed by the present invention utilizes the formation of a heterojunction to promote the electron transfer of black phosphorus with lone electron pairs, thereby achieving the effect of passivating black phosphorus. At the same time, the electron vacancy separation mechanism is utilized to enhance the potential barrier of the material and improve its sensitivity. Therefore, this type of BP-Au-MS2 ternary gas-sensitive composite material can achieve high-precision response to ppm-level target gas at room temperature, and has stronger material stability.

[0041] The use of this type of BP-Au-MS2 ternary gas-sensitive composite material to prepare various gas-sensitive elements can achieve higher accuracy, lower measurement concentration range, and longer service life. After experimental testing, the BP-Au-MS2 ternary gas-sensitive composite material of the present invention can detect 5ppb level NO2 at room temperature.

[0042] In the preparation process of the ternary BP-Au-MS2 ternary gas-sensitive composite material provided by the present invention, a transition metal sulfide with a mass inflorescence structure is first generated by a high-temperature reaction, and then black phosphorus is grown on the transition metal sulfide by induction of gold particles to form a heterojunction. The final prepared composite material has a higher crystallinity and the crystal structure is not destroyed, so it has a higher activity. In addition, the preparation method provided by the present invention does not require the use of complex processes such as liquid nitrogen freezing and inert gas protection, and the heterojunction growth process is achieved by a sintering method, so it is easier to carry out large-scale production and has stronger practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a scanning electron microscope image of the transition metal sulfide WS2 prepared in Examples 1-3 of the present invention.

[0044] Figure 2 This is a transmission electron microscope image of the ternary BP-Au-MS2 ternary gas-sensitive composite material BP-Au-MS2 prepared in Examples 1-3 of the present invention.

[0045] Figure 3 In the response and recovery characteristic experiment of the sensitive electrode of Test Example 2 of the present invention to target gases of different concentrations, the response curve of the sensitive electrode prepared by BP-Au-MS2 to NO2 gases of different concentrations is shown.

[0046] Figure 4 It is a line graph showing the time series changes of the response signal intensity of the reaction test group and the control group to the target gas with the same concentration in the accuracy and life test experiment of the gas sensor of Test Example 2 of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings, embodiments and test examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0048] Example 1

[0049] This embodiment prepares a new type of BP-Au-MS2 ternary gas-sensitive composite material, which is a ternary composite material containing gold, black phosphorus and transition metal sulfide. Specifically, the preparation method of this type of BP-Au-MS2 ternary gas-sensitive composite material is as follows:

[0050] (1) Prepare 1.6 g of sodium tungstate dihydrate, 1.76 g of oxalic acid, and 2.88 g of thiourea. Add sodium tungstate dihydrate to 100 ml of deionized water and stir to dissolve. Adjust the pH of the solution to 1.2 with hydrochloric acid and continue stirring for 15 min. Then, add oxalic acid to the solution and stir for 10 min, then add thiourea and stir for 30 min to obtain a uniformly mixed reaction system.

[0051] (2) The reaction system in the previous step was transferred to a reactor and reacted at 220° C. for 24 h. Then, the precipitate generated by the reaction was centrifuged and washed, and vacuum dried in a vacuum oven at 60° C. for 8 h to obtain a transition metal sulfide (WS2).

[0052] (3) Add the transition metal sulfide of the previous step to a sufficient amount of ethanol solution, and add HAuCl4 in a mass ratio of HAuCl4 to transition metal sulfide of 5:1. Use a vacuum disperser to ultrasonically treat the mixture for 2 hours and then stir for 8 to 12 hours. The ultrasonic power of the ultrasonic disperser is 300W to 500W and the frequency is 40KHz.

[0053] After the ultrasonic dispersion is completed, the mixture is centrifuged and washed to obtain a solid, and the solid is dried in a vacuum oven at a drying temperature of 60° C. for 8 h to obtain a gold-containing transition metal sulfide powder (Au-WS2).

[0054] (4) Mix 500 mg of the transition metal sulfide obtained in the above step with 500 mg of red phosphorus, 50 mg of solid iodine, and 12.5 mg of selenium powder. Send the mixture to a quartz tube and evacuate and seal it, then place the quartz tube in a muffle furnace for firing. The temperature control conditions of the firing process are as follows: first increase the temperature to 590-620°C at 5°C / min and keep it for 2h, then reduce the temperature to 500°C at 0.6-0.8°C / min and keep it for 5h, then reduce the temperature to 200°C at 1°C / min, and finally cool it naturally to obtain the BP-Au-MS2 ternary gas-sensitive composite material.

[0055] Example 2

[0056] This embodiment prepares a new type of BP-Au-MS2 ternary gas-sensitive composite material, which is a ternary composite material containing gold, black phosphorus and transition metal sulfide. Specifically, the preparation method of this type of BP-Au-MS2 ternary gas-sensitive composite material is as follows:

[0057] (1) Prepare 1.6 g of tungsten chloride, 1.92 g of oxalic acid, and 3.2 g of thiourea. Add tungsten chloride to 100 ml of deionized water and stir to dissolve. Adjust the pH of the solution to 1.5 with hydrochloric acid and continue stirring for 15 min. Then, add oxalic acid to the solution and stir for 10 min, then add thiourea and stir for 30 min to obtain a uniformly mixed reaction system.

[0058] (2) The reaction system in the previous step was transferred to a reactor and reacted at 220° C. for 24 h. Then, the precipitate generated by the reaction was centrifuged and washed, and vacuum dried in a vacuum oven at 60° C. for 8 h to obtain a transition metal sulfide (WS2).

[0059] (3) Add the transition metal sulfide of the previous step to a sufficient amount of ethanol solution, and add HAuCl4 in a mass ratio of HAuCl4 to transition metal sulfide of 5:1. Use a vacuum disperser to ultrasonically treat the mixture for 2 hours and then stir for 12 hours. The ultrasonic power of the ultrasonic disperser is 300W to 500W and the frequency is 40KHz.

[0060] After the ultrasonic dispersion is completed, the mixture is centrifuged and washed to obtain a solid, and the solid is dried in a vacuum oven at a drying temperature of 60° C. for 8 h to obtain a gold-containing transition metal sulfide powder (Au-WS2).

[0061] (4) Mix 500 mg of the transition metal sulfide obtained in the above step with 250 mg of red phosphorus, 25 mg of solid iodine, and 7 mg of selenium powder. Send the mixture to a quartz tube and evacuate and seal it, then place the quartz tube in a muffle furnace for firing. The temperature control conditions of the firing process are as follows: first increase the temperature to 600°C at 5°C / min and keep it for 2h, then reduce the temperature to 500°C at 0.7°C / min and keep it for 5h, then reduce the temperature to 200°C at 1°C / min, and finally cool it naturally to obtain the BP-Au-MS2 ternary gas-sensitive composite material.

[0062] Example 3

[0063] This embodiment prepares a new type of BP-Au-MS2 ternary gas-sensitive composite material, which is a ternary composite material containing gold, black phosphorus and transition metal sulfide. Specifically, the preparation method of this type of BP-Au-MS2 ternary gas-sensitive composite material is as follows:

[0064] (1) Prepare 2 g of sodium molybdate dihydrate, 2 g of oxalic acid, and 3.4 g of thiourea. Add sodium molybdate dihydrate to 100 ml of deionized water and stir to dissolve. Adjust the pH of the solution to 1.4 with hydrochloric acid and continue stirring for 15 min. Then, add oxalic acid to the solution and stir for 10 min, then add thiourea and stir for 30 min to obtain a uniformly mixed reaction system.

[0065] (2) The reaction system in the previous step was transferred to a reactor and reacted at 220° C. for 24 h. Then, the precipitate generated by the reaction was centrifuged and washed, and vacuum dried in a vacuum oven at 60° C. for 8 h to obtain a transition metal sulfide (WS2).

[0066] (3) Add the transition metal sulfide from the previous step to a sufficient amount of ethanol solution, and add HAuCl4 at a mass ratio of HAuCl4 to transition metal sulfide of 5:1. Use a vacuum disperser to ultrasonically treat the mixture for 2 hours and then stir for 10 hours. The ultrasonic power of the ultrasonic disperser is 300W to 500W and the frequency is 40KHz.

[0067] After the ultrasonic dispersion is completed, the mixture is centrifuged and washed to obtain a solid, and the solid is dried in a vacuum oven at a drying temperature of 60° C. for 8 h to obtain a gold-containing transition metal sulfide powder (Au-WS2).

[0068] (4) Mix 250 mg of the transition metal sulfide obtained in the above step with 375 mg of red phosphorus, 37.5 mg of solid iodine, and 19 mg of selenium powder. The mixture is sent to a quartz tube and sealed by vacuum, and then the quartz tube is placed in a muffle furnace for firing. The temperature control conditions of the firing process are as follows: first increase the temperature to 620°C at 5°C / min and keep it for 2h, then reduce the temperature to 500°C at 0.8°C / min and keep it for 5h, then reduce the temperature to 200°C at 1°C / min, and finally cool naturally to obtain the BP-Au-MS2 ternary gas-sensitive composite material.

[0069] Test Example 1

[0070] During the sample preparation process in Examples 1-3, technicians also used a scanning electron microscope (SEM) to scan the transition metal sulfide WS2 obtained in step (2) of Examples 1-3, and observed the microstructure of the intermediate product as follows: Figure 1 As shown, observe Figure 1 It can be seen that the microstructure of the transition metal sulfide obtained in this embodiment is similar to the clustered inflorescence structure of ping-pong chrysanthemum. This structure has a larger specific surface area, can provide more sites for gas adsorption, and also provide binding sites for gold particles and heterojunction growth, and the composite effect of the material is good.

[0071] Furthermore, in this experiment, the technicians also used a transmission electron microscope (TEM) to observe the submicrostructure of the BP-Au-MS2 ternary gas-sensitive composite material obtained in step (4). The results are as follows: Figure 2 As shown. Figure 2In the figure, the (111) crystal plane of BP, the (111) crystal plane of Au and the (105) crystal plane of WS2 can be clearly observed, indicating that a heterostructure of BP-Au-MS2 is formed, indicating that the embodiment scheme is feasible. At the same time, because of the construction of the heterostructure, BP can provide more electrons for WS2 and Au, preventing BP from providing electrons for O2 in the air, thereby achieving the purpose of anti-oxidation.

[0072] Example 4

[0073] Using the BP-Au-MS2 ternary gas-sensitive composite material prepared in Example 1, this example further prepares a sensitive electrode whose resistance changes with the change of the target gas concentration in the ambient atmosphere; the sensitive electrode includes a Pt interdigital electrode containing an alumina substrate, and a sensitive layer located on the surface of the Pt interdigital electrode. The material of the sensitive layer is the BP-Au-MS2 ternary gas-sensitive composite material finally obtained in Example 1.

[0074] The preparation method of the sensitive electrode is as follows: the BP-Au-MS2 ternary gas-sensitive composite material is added to anhydrous ethanol and ultrasonically dispersed for 5 minutes, and then the suspension is dropped on a Pt interdigital electrode containing an alumina substrate, and the desired gas-sensitive element containing a sensitive layer is obtained after drying.

[0075] Test Example 2

[0076] 1. Experiment on the response and recovery characteristics of sensitive electrodes to target gases of different concentrations.

[0077] The sensitive electrode prepared in Example 4 can achieve qualitative or quantitative detection of NO, NO2 or NH3 at ppb level under room temperature. In particular, since the BP-Au-MS2 ternary gas-sensitive composite material is most sensitive to nitrogen dioxide, NO2 is selected as the target gas, and the prepared sensitive electrode is selected as the detection electrode to form a dynamic four-channel gas-sensitive test system, and then the dynamic four-channel gas-sensitive test system is used as a NO2 concentration detector to determine the gas response function of the sensitive electrode to different concentrations of NO2 gas by cycling NO, NO2 or NH3.

[0078] The gas response function is generated as follows:

[0079] S1: Prepare the gas sensor in Example 4; and use the gas sensor as a detection electrode to form a dynamic four-channel gas sensing test system.

[0080] S2: Create a sealed gas detection environment and place the detection electrodes of the dynamic four-channel gas sensitive test system in the gas detection environment.

[0081] S3: According to the preset NO2 concentration measurement points, the dynamic four-channel gas-sensitive test system is used to cycle the response and recovery test to obtain the response-recovery curve. The response and recovery test includes the following process:

[0082] S31: Set multiple discrete measuring points according to the measuring range of the NO2 concentration detector; each measuring point includes a corresponding NO2 concentration Q i .

[0083] S32: According to NO2 concentration Q i The measuring points are sorted from small to large to obtain a measuring point queue to be filled.

[0084] S33: In the initial state, the gas filled in the gas detection environment is air, and the initial resistance value Ra of the detection electrode at the current moment is recorded. i .

[0085] S34: Select the initial measuring point of the measuring point queue as the current measuring point, and fill NO2 into the gas detection environment until the gas concentration reaches the NO2 concentration Q at the current measuring point. i Observe the decrease in the resistance of the detection electrode and record the lowest resistance value Rg under the current gas detection state. i . Complete the measurement task of the current measuring point and replace the gas in the gas detection environment with air.

[0086] S34: Select the next measuring point in the measuring point array queue as the current measuring point, repeat steps S33-S35, and execute the cycle to measure Ra in the air. i , measure Rg when NO2 reaches the current measuring point i The operation is repeated until the measurement tasks of all measuring points in the measuring point queue are completed.

[0087] At this time, the recorded resistance change waveform of the detection electrode is the required response-recovery curve.

[0088] S4: According to the data corresponding to each measuring point in the response-recovery curve in the previous step, the resistance change rate S corresponding to each measuring point is calculated by the following formula: i :

[0089]

[0090] S4: Based on the Q of a series of discrete measurement points obtained from the response-recovery curve i and S i The mapping relationship between them is used to fit a corresponding gas response function. The form of the gas response function is as follows:

[0091]

[0092] In the above formula, Q represents the detection result output by the NO2 concentration detector in real time, R represents the real-time resistance value of the detection electrode, R0 represents the resistance value of the detection electrode in the air; S represents the resistance change rate of the detection electrode under the current environment.

[0093] Finally, the response recovery curves of the sensitive electrode in Example 4 to different concentrations of NO2 gas measured in this test example are as follows: Figure 3 Analysis Figure 3 From the data in, it can be seen that the resistance of the sensitive electrode prepared in this embodiment decreases continuously with the increase of the concentration of the target gas (NO2), and when the concentration of the target gas decreases until it disappears, the resistance of the sensitive electrode will gradually recover to the initial value. In other words, the response of the sensitive electrode designed in this embodiment to target gases of different concentrations is reversible, and the "property strain" of the sensitive electrode with target gases of different concentrations is recoverable. Therefore, the sensitive electrode can be used as a gas sensor to realize online monitoring of the target gas concentration.

[0094] according to Figure 3 It can be seen from the data that as long as a mapping relationship is established between the resistance drop of the sensitive electrode and the corresponding concentration of the target gas, the corresponding gas concentration monitor can be designed through the sensitive element. For example, this test example writes the obtained gas response function into the data processing module of the dynamic four-channel gas-sensitive test system, and selects the gas-sensitive element of Example 4 as the detection electrode. Then this type of dynamic four-channel gas-sensitive test system becomes a NO2 concentration detector that can quantitatively measure the NO2 concentration. In addition, it should be emphasized that: considering that the BP-Au-MS2 ternary gas-sensitive composite material in Examples 1-3 has a strong sensitivity to NO, NO2 or NH3, it is also possible to obtain the gas response function of the prepared sensitive electrode to NO or NH3 through testing, and design the corresponding NO concentration detector and NH3 concentration detector.

[0095] 2. Accuracy and life test experiment of gas sensor

[0096] In addition to being able to achieve high-precision response to lower concentration trace-level target gases at room temperature, another advantage of the airtight composite material and gas sensor prepared in this embodiment is that it can improve the disadvantage of easy oxidation and degeneration of conventional gas-sensitive materials (such as black phosphorus material: BP) in the air, and improve the accuracy stability and service life of the sensitive element. In view of this feature, this test example further designed the following test experiment.

[0097] In the experiment, technicians selected conventional flaky black phosphorus materials as the sensitive layer to prepare the sensitive electrode of the control group, namely control group 1. And two groups of sensitive electrodes in Example 4 were selected as test group electrodes, namely test group 1 and test group 2. Then, the sensitive electrodes of the control group and the test group were used to construct a NO2 concentration detector; the sensitive electrodes of the control group were used to measure 50ppm of NO2 gas; the sensitive electrodes of test group 1 and test group 2 measured 0.05ppm and 1ppm of NO2 gas respectively; at intervals of 5d, the changes in the response signals of the sensitive electrodes of the three detection systems to the target gas within 30d were recorded respectively, and the data obtained are as follows: Figure 4 As shown,

[0098] analyze Figure 4 From the data, we can see that the signals of the sensitive electrodes in the test group and the control group fluctuate greatly in the early stage of the test, and the test signals will gradually decrease over time, that is, they are in an unstable period. This may be related to the surface oxidation of the sensitive layer material in the sensitive electrode. However, after a period of "natural aging", it can be seen that the test signals of each sensitive electrode gradually return to stability. At this time, the response state between the electrical properties of the sensitive electrode and the concentration of the target gas to be measured can remain constant, and the stable period is the period in which each sensitive electrode can work effectively, and the length of the stable period is the service life of the product.

[0099] Further integration Figure 4 Analysis of the service life of the three samples shows that the sensitive electrode of the control group could no longer obtain effective measurement signals after 20 days, which means that the sensitive electrode of the control group had failed after 20 days, and the effective service life of the product was from the 5th day to the 20th day, a total of 15 days. The reason for this phenomenon is that black phosphorus materials are prone to redox reactions in the air and gradually degrade.

[0100] In this embodiment, test group 1 entered the stable period on the 15th day, and valid test signals could still be collected on the 30th day, and test group 2 entered the stable period on the 10th day, and valid test signals could still be collected on the 30th day. This shows that the BP-Au-MS2 composite material developed in this embodiment can effectively overcome the defect of easy degradation of conventional BP materials, improve the oxidation resistance of the materials, and solve the problem that the performance of BP-type gas sensors is unstable in the air.

[0101] Combination Figure 4 The data also confirm that the experimental groups 1 and 2 have longer effective lifespans than the control group. The BP-Au-MS2 composite material of this embodiment can effectively expand the practical application of BP material sensitive elements in other aspects, such as being a photoelectric device that can operate stably for a long time in the air.

[0102] Example 5

[0103] This embodiment provides a harmful gas alarm, which is one of the typical applications of the BP-Au-MS2 ternary gas-sensitive composite material in Embodiments 1-3. The harmful gas alarm provided in this embodiment is used to monitor the combined concentration of ammonia and nitrogen oxide gases in the target space in real time, and to sound an alarm when the concentration detection value exceeds a preset upper limit. The harmful gas alarm includes: a sensitive element, a detection circuit, a data processing module, and an alarm device.

[0104] Among them, the sensitive element adopts the gas sensitive element as mentioned above. The detection circuit is used to collect the real-time resistance value of the sensitive element. The data processing module includes a calculation unit and a comparison unit. The calculation unit is used to calculate the resistance change rate S of the current state of the sensitive element relative to the initial state according to the real-time resistance value collected by the detection circuit. The comparison unit is used to compare whether the resistance change rate S is a preset safety upper limit Smax. When S>Smax, a warning signal is output, and when S≤Smax, a safety signal is output. The alarm device is used to receive the output signal of the comparison unit in the data processing module, and when the received output signal is a warning signal, it sends an alarm indicating that the concentration of dangerous gas exceeds the limit.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A BP-Au-MS2 ternary gas-sensitive composite material, characterized in that: It is a ternary composite material containing gold, black phosphorus and transition metal sulfide; the preparation method of the BP-Au-MS2 ternary gas-sensitive composite material is as follows: (1) preparing a transition metal salt, oxalic acid, and thiourea in a mass ratio of 1:(1-1.5):(1.7-2); adding the transition metal salt to a sufficient amount of deionized water and stirring to dissolve, and adjusting the pH of the solution to 1.2-1.5 with hydrochloric acid and continuing to stir for 15 minutes; then, adding oxalic acid to the above solution and stirring for 10 minutes, and then adding thiourea and stirring for 30 minutes to obtain a uniformly mixed reaction system; The transition metal salt is selected from any one of sodium tungstate dihydrate, tungsten chloride, and sodium molybdate dihydrate; (2) The reaction system in the previous step was transferred to a reactor and reacted at a temperature of 220-250°C for 24 hours; the precipitate generated by the reaction was centrifuged and washed, and vacuum dried for 8 hours to obtain transition metal sulfide MS2; (3) adding the transition metal sulfide prepared in the previous step to a sufficient amount of ethanol solution, and adding HAuCl4 in a mass ratio of HAuCl4 to transition metal sulfide of 5:1; subjecting the mixture to ultrasonic treatment for 2 h and then stirring for 8-12 h; centrifuging and washing to obtain a solid, and vacuum drying for 8 h to obtain a gold-containing transition metal sulfide powder; (4) The gold-containing transition metal sulfide obtained in the previous step is mixed evenly with red phosphorus, solid iodine, and selenium powder in a mass ratio of 1: (0.5-2): (0.05-0.2): (0.025-0.1); the mixture is vacuum-fired, and the temperature control conditions of the vacuum firing process are as follows: first, the temperature is increased to 590-620°C at 5°C / min and kept for 2h, and then the temperature is decreased to 500°C at 0.6-0.8°C / min and kept for 5h, and then the temperature is decreased to 200°C at 1°C / min, and finally naturally cooled to obtain the BP-Au-MS2 ternary gas-sensitive composite material.

2. The BP-Au-MS2 ternary gas-sensitive composite material according to claim 1, characterized in that: The vacuum drying process of the product in steps (2) and (3) is completed in a vacuum oven, and the drying temperature is set to 60°C.

3. The BP-Au-MS2 ternary gas-sensitive composite material according to claim 1, characterized in that: In step (3), the mixture containing transition metal sulfide, HAuCl4 and ethanol solution is subjected to ultrasonic dispersion treatment by an ultrasonic disperser, and the ultrasonic power of the ultrasonic disperser is 300W~500W and the frequency is 40KHz.

4. The BP-Au-MS2 ternary gas-sensitive composite material according to claim 1, characterized in that: In step (4), the vacuum firing method of the mixture of the transition metal sulfide containing gold and red phosphorus, solid iodine and selenium powder is as follows: the mixture is sent to a quartz tube and vacuum-sealed, and then the quartz tube is placed in a muffle furnace for firing.

5. An application of the BP-Au-MS2 ternary gas-sensitive composite material as claimed in any one of claims 1 to 4, characterized in that: The gas-sensitive composite material is used to prepare a gas-sensitive probe or a trace gas detection element, and qualitative or quantitative detection of ppb-level target gas is achieved under room temperature.

6. The use of the BP-Au-MS2 ternary gas-sensitive composite material as claimed in claim 5, characterized in that: The target gas includes nitrogen oxide gas and ammonia gas.

7. The use of the BP-Au-MS2 ternary gas-sensitive composite material as claimed in claim 6, characterized in that: The target gas is NO2.

8. A gas sensor, characterized in that: It is a sensitive electrode whose resistance changes with the change of the concentration of the target gas in the ambient atmosphere; the sensitive electrode comprises a Pt interdigital electrode containing an alumina substrate, and a sensitive layer located on the surface of the Pt interdigital electrode; the material of the sensitive layer is the BP-Au-MS2 ternary gas-sensitive composite material as claimed in any one of claims 1 to 4; wherein the preparation method of the gas sensor is as follows: The BP-Au-MS2 ternary gas-sensitive composite material is added to ethanol and subjected to ultrasonic dispersion treatment for 1 to 5 minutes. The suspension is then dropped onto a Pt interdigital electrode containing an alumina substrate, and the desired gas-sensitive element containing a sensitive layer is obtained after drying.

9. A NO2 concentration detector, characterized in that: It uses the gas sensor as claimed in claim 8 as a detection electrode to form a dynamic four-channel gas-sensitive test system; the data processing module in the NO2 concentration detector outputs the currently detected NO2 concentration value according to the acquired real-time resistance value R of the detection electrode and the pre-constructed gas response function Q; in the NO2 concentration detector, the method for generating the gas response function is as follows: S1: preparing the gas sensor as claimed in claim 8; and using the gas sensor as a detection electrode to form a dynamic four-channel gas sensing test system; S2: creating a sealed gas detection environment, and placing the detection electrodes of the dynamic four-channel gas-sensitive test system in the gas detection environment; S3: According to different preset NO2 concentration measurement points, the dynamic four-channel gas-sensitive test system is used to cyclically perform response and recovery tests to obtain a response-recovery curve; the response and recovery test includes the following process: S31: Set multiple discrete measuring points according to the measuring range of the NO2 concentration detector; each measuring point includes a corresponding NO2 concentration Q i ; S32: According to NO2 concentration Q i Sort the measurement points in ascending order to obtain a measurement point queue to be filled; S33: In the initial state, the gas filled in the gas detection environment is air, and the initial resistance value of the detection electrode at the current moment is recorded. Ra i ; S34: Select the initial measuring point of the measuring point queue as the current measuring point, and fill NO2 into the gas detection environment until the gas concentration reaches the NO2 concentration at the current measuring point. Q i ; Observe the decrease in the resistance of the detection electrode and record the lowest resistance value under the current gas detection state R i ; Complete the measurement task of the current measuring point and replace the gas in the gas detection environment with air; S34: Select the next measuring point in the measuring point array queue as the current measuring point, repeat steps S33-S35, and execute the measurement in the air in a loop. Ra i , measured when NO2 reaches the current measuring point R i The operation is repeated until the measurement tasks of all the measurement points in the measurement point queue are completed; At this time, the recorded resistance change waveform of the detection electrode is the required response-recovery curve; S4: Based on the data corresponding to each measuring point in the response-recovery curve in the previous step, calculate the resistance change rate corresponding to each measuring point by the following formula: S i : S4: Based on a series of discrete measurement points obtained from the response-recovery curve Q i and S i The mapping relationship between them is used to fit a corresponding gas response function, and the form of the gas response function is as follows: In the above formula, Q It indicates the real-time output of the NO2 concentration detector. R Indicates the real-time resistance value of the detection electrode. R 0 Indicates the resistance value of the detection electrode in the air; S Indicates the resistance change rate of the detection electrode under the current environment.

10. A harmful gas alarm, characterized in that: It is used to monitor the comprehensive concentration of ammonia and nitrogen oxide gases in the target space in real time, and issue an alarm when the concentration detection value exceeds the preset upper limit; the harmful gas alarm includes: A sensitive element, which adopts the gas sensitive element as claimed in claim 8; A detection circuit, which is used to collect the real-time resistance value of the sensitive element; The data processing module includes a calculation unit and a comparison unit. The calculation unit is used to calculate the resistance change rate S of the current state of the sensitive element relative to the initial state according to the real-time resistance value collected by the detection circuit; the comparison unit is used to compare the resistance change rate S Is there a preset safety limit? Smax ,when S > Smax Then an early warning signal is output. S ≤ Smax Then a safety signal is output; and The alarm device is used to receive the output signal of the comparison unit in the data processing module, and to issue an alarm indicating that the concentration of dangerous gas exceeds the limit when the received output signal is a warning signal.

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